To me I think most of MAC's issues were caused by him not racking the gun hard enough. You can see on many of the reloads he had trouble with he racked the pump slowly or didn't slam it back to release the next shell from the tube.
With my KSG you definitely need to rack it hard or it only ejects the empty and doesn't release the next shell.
I also watched his RFB videos where he had problems and to me it didn't sound like he understands how the gas system works and therefore doesn't understand how to adjust it correctly.
sapper043, What type of vertical grip were you using?